Non-uniform electron density estimation based on electromagnetic wave attenuation in plasma

The surface of a high-speed vehicle reentering the atmosphere is surrounded by plasma sheath.Due to the influence of the inhomogeneous flow field around the vehicle,understanding the electromagnetic properties of the plasma sheath can be challenging.Obtaining the electron density of the plasma sheath is crucial for understanding and achieving plasma stealth of vehicles.In this work,the relationship between electromagnetic wave attenuation and electron density is deduced theoretically.The attenuation distribution along the propagation path is found to be proportional to the integral of the plasma electron density.This result is used to predict the electron density profile.Furthermore,the average electron density is obtained using a back-propagation neural network algorithm.Finally,the spatial distribution of the electron density can be determined from the average electron density and the normalized derivative of attenuation with respect to the propagation depth.Compared to traditional probe measurement methods,the proposed approach not only improves efficiency but also preserves the integrity of the plasma environment.

Diagnosing ratio of electron density to collision frequency of plasma surrounding scaled model in a shock tube using low-frequency alternating magnetic field phase shift

A non-contact low-frequency(LF)method of diagnosing the plasma surrounding a scaled model in a shock tube is proposed.This method utilizes the phase shift occurring after the transmission of an LF alternating magnetic field through the plasma to directly measure the ratio of the plasma loop average electron density to collision frequency.An equivalent circuit model is used to analyze the relationship of the phase shift of the magnetic field component of LF electromagnetic waves with the plasma electron density and collision frequency.The applicable range of the LF method on a given plasma scale is analyzed.The upper diagnostic limit for the ratio of the electron density(unit:m^(-3))to collision frequency(unit:Hz)exceeds 1×10^(11),enabling an electron density to exceed 1×10^(20)m^(-3)and a collision frequency to be less than 1 GHz.In this work,the feasibility of using the LF phase shift to implement the plasma diagnosis is also assessed.Diagnosis experiments on shock tube equipment are conducted by using both the electrostatic probe method and LF method.By comparing the diagnostic results of the two methods,the inversion results are relatively consistent with each other,thereby preliminarily verifying the feasibility of the LF method.The ratio of the electron density to the collision frequency has a relatively uniform distribution during the plasma stabilization.The LF diagnostic path is a loop around the model,which is suitable for diagnosing the plasma that surrounds the model.Finally,the causes of diagnostic discrepancy between the two methods are analyzed.The proposed method provides a new avenue for diagnosing high-density enveloping plasma.

Electron density measurement by the three boundary channels of HCOOH laser interferometer on the HL-3 tokamak

Far-infrared(FIR)interferometer is widely used to measure the electron density in the magnetically confined fusion plasma devices.A new FIR laser interferometer with a total of 13 channels(8 horizontal channels and 5 oblique channels)is under development on the HL-3tokamak by using the formic-acid laser(HCOOH,f=694 GHz).In order to investigate the boundary electron density activity during the divertor discharge,three horizontal interferometry channels located at Z=-97,-76,76.5 cm have been successfully developed on HL-3 in 2023,and put into operation in recent experimental campaign,with a time resolution of<1.0μs and lineintegrated electron density resolution of~7.0×10^(16) m^(-2).This paper mainly focuses on the optical design of the three-channel interferometry system,as well as optical elements and recent experimental result on HL-3.

The nature of electron density enhancement over a wide altitude range during ionosphere heating experiments at EISCAT

During the course of ionospheric heating experiments, researchers at the European Incoherent Scatter Scientific Association (EISCAT) observed an apparent electron density enhancement. The enhancement extended over a wide range of altitudes, above the reflection altitude of the high-frequency pump wave. However, whether this enhancement actually corresponds to a true enhancement in electron density remains an open question. When the dispersion relation of ion acoustic waves is followed, the frequency ratio of the enhanced ion line to the background ion line suggests that the profile of the effective ion mass may have remained unchanged. Furthermore, the solar radio flux and ion drift velocity indicate no significant changes in the ion species and their densities. In conclusion, the electron density enhancement observed at EISCAT should not, in fact, be considered a true enhancement.

Oxygen Vacancy-induced Electron Density Tuning of Fe_(3)O_(4) for Enhanced Oxygen Evolution Catalysis

Despite the tremendous efforts devoted to enhancing the activity of oxygen evolution reaction(OER)catalysts,there is still a huge challenge to deeply understand the electronic structure characteristics of transition metal oxide to guide the design of more active catalysts.Herein,Fe_(3)O_(4)with oxygen vacancies(Fe_(3)O_(4)-Vac)was synthesized via Ar ion irradiation method and its OER activity was greatly improved by properly modulating the electron density around Fe atoms.The electron density of Fe_(3)O_(4)-Vac around Fe atoms increased compared to that of Fe_(3)O_(4)according to the characterization of synchrotron-based X-ray absorption near-edge structure(XANES),extended X-ray absorption fine structure(EXAFS)spectra,and density functional theory(DFT)calculation.Moreover,the DFT results indicate the enhancement of the desorption of HOO^(*)groups which significantly reduced the OER reaction barrier.Fe_(3)O_(4)-Vac catalyst shows an overpotential of 353 m V,lower than that of Fe OOH(853 m V)and Fe_(3)O_(4)(415 m V)at 10 m A cm^(-2),and a low Tafel slope of 50 m V dec^(-1)in 1 M KOH,which was even better than commercial RuO_(2)at high potential.This modulation approach provides us with valuable insights for exploring efficient and robust water-splitting electrocatalysts.

Electron Density and Optical Emission Measurements of SF_6/O_2 Plasmas for Silicon Etch Processes

This work investigates internal plasma process parameters using a hairpin resonance probe and optical emission spectroscopy. The dependence of electron density and atomic fluorine on the percentage of oxygen in an SF6/O2 discharge was measured using these methods. An RIE Oxford Instruments 80 plus chamber was used for the experiments. Two different process powers （100 W and 300 W） at a constant pressure （100 mTorr） were used, and it was found that the optical emission intensity of the 703.7 nm and 685.6 nm lines of atomic fluorine increased rapidly as oxygen was added to the SF6 discharge, reached their maximum at an O2 fraction of 20% and then decreased with further addition of oxygen. The plasma electron density was also strongly influenced by the addition of O2.

Research on the Real-Time Phase Jump Process Method for Plasma Electron Density Measurement in HL-2A Tokamak

In the real-time plasma electron density measurement using far infrared （FIR） laser interferometry, the plasma electron density can be calculated by measuring the real time phase difference between the reference signal and the probe signal. A novel Real-time Phase Jump Process （RPJP） method is applied to the HL-2A tokamak. With this method, the phase difference 1 precision is up to 1/3600 fringe （1 fringe is equal to a phase shift of 2π）, and the dynamic measure- ment range is extensible 65536 fringes. The time resolution of the phase difference is 80 ns, while the feedback delay is 180 its.

Atomic Emission Spectra Diagnosis and Electron Density Measurement of Semiconductor Bridge (SCB) Plasma

Emission spectra of a semiconductor bridge （SCB） plasma in a visible range was studied in air. The electron density was measured in a conventional way from the broadening of the Al Ⅰ 394.4 nm Stark width. Based on the Saha equation, a system for recording the intensity of Si Ⅰ 390.5 nm and Si Ⅱ 413.1 nm was designed. With this technique, the SCB plasma electron density was measured well and accurately. Moreover, the electron density distribution Vs time was acquired from one SCB discharge. The individual result from the broadening of the Al Ⅰ 394.4 nm Stark width and Saha equation was all in the range of 1015 cm^-3 to 1016 cm^-3. Finally the presumption of the local thermodynamic equilibrium （LTE） condition was validated.

Measurement of electron density and electron temperature of a cascaded arc plasma using laser Thomson scattering compared to an optical emission spectroscopic approach

As advanced linear plasma sources, cascaded arc plasma devices have been used to generate steady plasma with high electron density, high particle flux and low electron temperature. To measure electron density and electron temperature of the plasma device accurately, a laser Thomson scattering（LTS） system, which is generally recognized as the most precise plasma diagnostic method, has been established in our lab in Dalian University of Technology. The electron density has been measured successfully in the region of 4.5？×10^19m^-3 to7.1？×10^20m^-3 and electron temperature in the region of 0.18 eV to 0.58 eV. For comparison,an optical emission spectroscopy（OES） system was established as well. The results showed that the electron excitation temperature（configuration temperature） measured by OES is significantly higher than the electron temperature（kinetic electron temperature） measured by LTS by up to 40% in the given discharge conditions. The results indicate that the cascaded arc plasma is recombining plasma and it is not in local thermodynamic equilibrium（LTE）. This leads to significant error using OES when characterizing the electron temperature in a non-LTE plasma.

Plasma Electron Density Measuring and Processing on the J-TEXT Tokamak

Plasma electron density is one of the most fundamental parameters in the study of tokamak plasma physics.The method of plasma electron density measuring and processing on the Joint Texas Experimental Tokamak(J-TEXT) was presented in this paper.The principle of the plasma electron density measuring by hydrogen cyanide(HCN) laser interferometer was introduced.Room temperature triglycine sulface(TGS) detector was used to obtain the beat signal of HCN,and phase difference was measured by high-speed acquisition card DAQ2010.Based on the signal characteristics,a specific HCN processing algorithm was designed to eliminate the baseline offset accurately and process overturns of HCN signals effectively.As a result,plasma electron density with high accuracy and low noise has been obtained during the J-TEXT tokamak experiment.

Measurement of time-varying electron density of the plasma generated from a small-size cylindrical RDX explosion by Rayleigh microwave scattering

It is challenging to measure the electron density of the unsteady plasma formed by charged particles generated from explosions in the air,because it is transient and on a microsecond time scale.In this study,the time-varying electron density of the plasma generated from a small cylindrical cyclotrimethylenetrinitramine(RDX)explosion in air was measured,based on the principle of microwave Rayleigh scattering.It was found that the evolution of the electron density is related to the diffusion of the detonation products.The application of the Rayleigh microwave scattering principle is an attempt to estimate the electron density in explosively generated plasma.Using the equivalent radius and length of the detonation products in the bright areas of images taken by a high-speed framing camera,the electron density was determined to be of the order of 10^(20)m^(−3).The delay time between the initiation time and the start of variation in the electron-density curve was 2.77–6.93μs.In the time-varying Rayleigh microwave scattering signal curve of the explosively generated plasma,the electron density had two fluctuation processes.The durations of the first stage and the second stage were 11.32μs and 19.20μs,respectively.Both fluctuation processes increased rapidly to a peak value and then rapidly attenuated with time.This revealed the movement characteristics of the charged particles during the explosion.

Electron density distribution of LiMn_(2)O_(4)cathode investigated by synchrotron powder x-ray diffraction

Electron density plays an important role in determining the properties of functional materials.Revealing the electron density distribution experimentally in real space can help to tune the properties of materials.Spinel Li Mn2 O4 is one of the most promising cathode candidates because of its high voltage,low cost,and non-toxicity,but suffers severe capacity fading during electrochemical cycling due to the Mn dissolution.Real-space measurement of electron distribution of Li Mn2 O4 experimentally can provide direct evaluation on the strength of Mn–O bond and give an explanation of the structure stability.Here,through high energy synchrotron powder x-ray diffraction(SPXRD),accurate electron density distribution in spinel Li Mn2 O4 has been investigated based on the multipole model.The electron accumulation between Mn and O atoms in deformation density map indicates the shared interaction of Mn–O bond.The quantitative topological analysis at bond critical points shows that the Mn–O bond is relatively weak covalent interaction due to the oxygen loss.These findings suggest that oxygen stoichiometry is the key factor for preventing the Mn dissolution and capacity fading.

Electron density calculation based on Stark broadening of D Balmer line from detached plasma in EAST tungsten divertor

The electron density within the volume of the tungsten divertor of the Experimental Advanced Superconducting Tokamak （EAST） is calculated based on Dε line （396.9 nm） Stark broadening （SB） measurements. The quasistatic approximation is employed in the SB calculation of the Dε line. The influences of other broadening mechanisms on the calculation error of electron density have been evaluated. The SB method is applied to the study of spatial distribution and time evolution of the electron density in the W divertor. Two electron density bands are observed in the detached divertor plasma during an L-mode discharge sustained by low hybrid wave （LHW） heating, which could be related to the striated particle flux distribution induced by LHW. After the onset of detachment, the upper electron density band corresponding to outer strike point firstly increases then decreases, while the lower density band corresponding to striated particle flux increases continually although the electron densities from Langmuir Probes at the divertor plate keep a descending trend. This could indicate a downward movement of the radiation region that approximately moves along the magnetic field lines after the onset of detachment.

Results of Ionospheric Heating Experiments Involving an Enhancement in Electron Density in the High Latitude Ionosphere

Observations are presented of the phenomenon of the enhancement in electron density and temperature that is caused by a powerful pump wave at a frequency near the fifth gyrofrequency. The observations show that the apparent enhancement in electron density extending over a wide altitude range and the enhancement in electron temperature around the reflection altitude occur as a function of pump frequency. Additionally, the plasma line spectra show unusual behavior as a function of pump frequency. In conclusion, the upper hybrid wave resonance excited by the pump wave plays a dominating role and leads to the enhancement in electron temperature at the upper hybrid altitude. The phenomenon of apparent enhancement in electron density does not correspond to the true enhancement in electron density, this may be due to some mechanism that preferentially involves the plasma transport process and leads to the strong backscatter of radar wave along the magnetic line, which remains to be determined.

An Indirect Method for Measuring Electron Density of Atmospheric Pressure Plasma Jets

An indirect method for measuring the electron density of radio frequency atmospheric pressure plasma jets （RF-APPJ） based on the discharge voltage and current waveforms is presented. An equivalent circuit of the plasma discharge is assumed by taking into account the electrode capacitance, serial resistance and inductance of the bulk plasma, as well as the sheath impedance. Based on the circuit model, the electron density can be obtained according to Ohm＇s law. By using this method, the effects of the electrode shape and discharge gap on the electron density are discussed.

Analysis of Anomalous Enhancement in TEC and Electron Density in the China Region Prior to the 17 March 2015 Geomagnetic Storm Based on Ground and Space Observations

Total Electron Content(TEC)and electron density enhancement were observed on the day before 17 March 2015 great storm in the China Region.Observations from ground-and space-based instruments are used to investigate the temporal and spatial evolution of the pre-storm enhancement.TEC enhancement was observed from 24°N to 30°N after 10:00 UT at 105°E,110°E and 115°E longitudes on March 16.The maximum magnitude of TEC enhancement was more than 10 TECU and the maximal relative TEC enhancement exceeded 30%.Compared with geomagnetic quiet days,the electron density of Equatorial Ionization Anomaly(EIA)northern peak from Swarm A/C satellites on March 16 was larger and at higher latitudes.NmF2 enhanced during 11:30—21:00 UT at Shaoyang Station and increased by 200%at~16:00 UT.However,TEC and electron density enhancement were not accompanied by a significant change of hmF2.Most research has excluded some potential mechanisms as the main driving factors for storm-time density enhancements by establishing observational constraints.In this paper,we observed pre-storm enhancement in electron density at different altitudes and Equatorial Electrojet(EEJ)strength results derived from ground magnetometers observations suggest an enhanced eastward electric field from the E region probably played a significant role in this event.

Anomaly of the ionospheric electron density close to earthquakes:Case studies of Pu'er and Wenchuan earthquakes

The electron density recorded onboard the DEMETER satellite was analyzed to search for possible anomalies before earthquakes both in space and time. To distinguish pre-earthquake anomalies from the other anomalies related to geomagnetic activity, data were filtered using the Kp index. The analysis is based on the comparison of data recorded closely to earthquakes in space and time and past data for the same area. In analyzing data around the time and location of the Pu＇er and Wenchuan earthquakes, obvious anomalies in electron density were found close to the epicenters, and some remarkable disturbances were detected before the earthquakes occurred. The results were finally compared with those of previous works that used the same data but employed different analysis methods. Good agreement was found which suggests that these anomalies have a close relation to the earthquake preparation.

Comparing two iteration algorithms of Broyden electron density mixing through an atomic electronic structure computation

By performing the electronic structure computation of a Si atom, we compare two iteration algorithms of Broyden electron density mixing in the literature. One was proposed by Johnson and implemented in the well-known VASP code.The other was given by Eyert. We solve the Kohn-Sham equation by using a conventional outward/inward integration of the differential equation and then connect two parts of solutions at the classical turning points, which is different from the method of the matrix eigenvalue solution as used in the VASP code. Compared to Johnson＇s algorithm, the one proposed by Eyert needs fewer total iteration numbers.

Variation of electron density in spectral broadening process in solid thin plates at 400 nm

The generation of continuous spectrum centered at 400 nm from solid thin plates is demonstrated in this work.A continuum covering 365 nm to 445 nm is obtained when 125-µJ frequency-doubled Ti:sapphire laser pulses are applied to six thin fused silica plates at 1-kHz repetition rate.The generalized nonlinear Schrodinger equation simplified for forward propagation is solved numerically,the spectral broadening with the experimental parameters is simulated,and good agreement between simulated result and experimental measurement is achieved.The variation of electron density in the thin plate and the advantage of a low electron density in the spectral broadening process are discussed.

Programmable electron density patterns induced by the interaction of an array laser and underdense plasma

The spatially modulated electron distribution of plasma is the basis for obtaining programmable electron density patterns.It has an important influence on plasma technology applications.We propose an efficient scheme to realize controllable electron density patterns in underdense plasma based on the array laser-plasma interaction.Theoretical evidence for the realization of programmable electron density patterns and the corresponding electrostatic field is provided analytically,which is confirmed by particle-in-cell simulations.Results show that the spatial distribution of electron density in the propagation and transverse directions of the laser can be highly modulated to obtain rich programmable electron density patterns by adjusting the array pattern code and pulse width of the array laser beam.